Seasonal Influenza Deaths More Common Worldwide Than Previously Thought

Up to 650,000 people in the world die from seasonal flu each year. This is much higher than the often-used numbers of 250,000 to 500,000 deaths cited by the World Health Organization (WHO) based on data thought to reach back decades, which did not take into account experience of developing countries. However, since then, many countries have improved their flu surveillance systems, and have been able to estimate deaths from the disease.

“These figures indicate the high burden of influenza and its substantial social and economic cost to the world,” said Dr. Peter Salama, executive director of WHO’s Health Emergencies Programme. “They highlight the importance of influenza prevention for seasonal epidemics, as well as preparedness for pandemics.”

The Global Seasonal Influenza-associated Mortality Collaborator Network, an international team from over 40 countries, included experts from the US Centers for Disease Control and Prevention (CDC), Pan American Health Organization (PAHO), All India Institute of Medical Science, South African National Institute of Communicable Diseases, Taiwan Centers for Disease Control, and Ministries of Health and universities published its findings with details of how they came up with the number in the latest issue of The Lancet.

The Poorest Regions & Elderly Are Most Affected

The team estimated excess deaths due to flu for 33 individual countries - 57 percent of the world’s population - based on surveillance data from 1999 up to 2015. The estimates were then extrapolated to 185 countries covering six WHO regions, four World Bank income classifications, and selected age-groups. Data from 14 countries were also used to validate estimates.

The researchers said the new estimate is higher, because the older numbers probably did not reflect the experience of some of the areas of the world with high flu mortality, underestimating the death burden. They noted, however, their new estimate may mask the true overall death burden, because the study focused on respiratory deaths related to flu, which does not consider the flu’s known exacerbating impact on other conditions often listed as causes of death, including cardiovascular disease or diabetes.

Results showed that the most deaths occur among people aged over 75 years (51.3 – 99.4 per 100, 000 individuals), and in the world’s poorest regions: sub-Saharan Africa (2.8 – 16.5 per 100, 000 individuals) and Southeast Asia (3.5 – 9.2 per 100, 000 individuals). Deaths were also high but slightly lower in Eastern Mediterranean and Southeast Asian countries.

According to the investigators, the new findings could assist countries that want to introduce or expand flu vaccination programs and could be used to help win more support from global health groups looking to increase access to the vaccines in low- and middle-income countries.

Significant Variation Among Nations

In a commentary in the same Lancet issue, Dr. Sheena Sullivan with the WHO Collaborating Center and Peter Doherty Institute for Infection and Immunity in Melbourne, Australia, said the study provides a much-needed and a more accurate update to the earlier WHO estimate. Having a global estimate is useful, she said, and the country-specific estimates in the new study are valuable, because they can be used by country decision-makers.

“Influenza vaccination programs exist in most high-income countries, but many low-income and lower-middle-income countries have no influenza vaccination policies in place. Often, no mortality estimates are available for low-income and lower-middle-income countries, where limited health-care infrastructure and the competing demands of other communicable and, increasingly, non-communicable diseases might dominate allocation of health resources.”

Important To Study Non-Respiratory Flu Deaths

Although the new estimates show influenza-associated deaths have increased, they might underestimate the true death toll from influenza because it does not include deaths attributable to non-respiratory causes. The authors also note that more research is needed to understand morality contributions of different seasonal flu strains, the death-reduction benefits of flu vaccination programs and flu’s known effect on other conditions including cardiovascular disease or diabetes. Influenza has been widely recognized as a trigger for other diseases. It can cause a wide range of complications, including pneumonia, bacterial co-infection, cardiovascular complications, and the worsening of diabetes.

Influenza has been widely recognized as a trigger for other diseases.

An annual seasonal flu vaccine is the best way to reduce people’s risk of getting sick with the flu and spreading it to others. The WHO recommends vaccinating people most susceptible to influenza infection, including young children, pregnant women, people with chronic medical conditions, and older adults.